TiO2 nanotube arrays: a study on the surface electrochemical reactions during the photoelectrochemical process

The surface electrochemical reactions of TiO2 nanotube arrays (NTAs) corresponding to different active species of TiO2 NTAs (center dot OH, h(+), and center dot O-2 (-)) play key roles during the photoelectrochemical process. Effect of the active species and surface electrochemical reactions are studied by adding capture agents of isopropyl alcohol (IPA) for center dot OH, ammonium oxalate ((NH4)(2)C2O2) for h(+), and benzoquinone (BQ) for center dot O-2 (-) radicals. The changes of photocurrent with addition of capture agents confirm the existence of center dot OH, h(+), and center dot O-2 (-) during photoelectrochemical process. IPA and (NH4)(2)C2O2 additions are found to enhance the photocurrent by accelerating the consumption velocity of h(+) indirectly and directly and restricting the chargers recombination. BQ can decrease the photocurrent stepwise to 0 due to the indirect consumption of e(-) on surface of TiO2 NTAs. The consumption of h(+) by forming center dot OH is 38% that of the whole consumption of h(+). The ratio of chargers recombination is higher than 80.8% that of the whole photogenerated chargers.